Multifilament extrusion method and apparatus

ABSTRACT

Apparatus for producing a multifilament strand wherein the strand is extruded downwardly in heat exchange relationship with a gas is improved according to the present invention by providing the gas as an upwardly flowing annular gas flow surrounding the downwardly flowing filaments. The gas is conducted upwardly parallel to the filaments and thus does not impinge laterally upon the filaments. The extruded filaments entrap ambient air which tends to remain entrained in the downwardly moving strand. The upwardly flowing annular gas stream tends to pull this entrained gas out of the downwardly moving filament thus effectively cooling the filament without causing adjacent strands to impinge upon one another. In this manner, the capacity of the apparatus is increased substantially. Fibers such as polypropylene can be melt spun according to the present invention by passing the molten extruded fibers downwardly inside an annular upwardly flowing heat exchange gas stream. As mentioned, this tends to remove entrained air from the downwardly moving filaments thus effectively rapidly cooling the filaments without causing them to impinge upon one another.

United States Patent Arav et al.

4 1 Aug. 22, 1972 [54] MULTIFILAMENT EXTRUSION METHOD AND APPARATUS [72] Inventors: Ronnie A. Arav, Netania, Israel; Gi-

anpietro Trentini, Pinerolo, Italy [52] US. Cl. ..264/I76 F, 18/8 QM [51] Int. Cl. ..B28b 3/20 [58] Field of Search ..l8/8 QM; 264/176 F [56] References Cited UNITED STATES PATENTS 2,252,684 8/1941" Babcock ..264/176F 3,611,485 10/1971 Leybourne etal........l8/8 on Primary Examiner-Jay H. Woo

' Attorney-Larson, Taylor and Hinds s71 ABSTRACT Apparatus for producing a multifilament strand EXTRUDER wherein the strand is extruded downwardly in heat exchange relationship with a gas is improved according to the present invention by providing the gas as an upwardly flowing annular gas flow surrounding the downwardly flowing filaments. The gas is conducted upwardly parallel to the filaments and thus does not impinge laterally upon the filaments. The extruded filaments entrap ambient air which tends to remain entrained in the downwardly moving strand. The upwardly flowing annular gas stream tends to pull this entrained gas out of the downwardly moving filament thus effectively cooling the filament without causing adjacent strands to impinge upon one another. In this manner, the capacity of the apparatus is increased substantially. Fibers such as polypropylene can be melt spun according to the present invention by passing the molten extruded fibers downwardly inside an annular upwardly flowing heat exchange gas stream. As mentioned, this tends to remove entrained air from the downwardly moving filaments thus effectively rapidly cooling the filaments without causing them to impinge upon one another.

12 Claims, 3 Drawing Figures BLOWER U HEAT EXCHANGER COOLANT PATENTED AUG 22 I972 EXTRUDER rzzrdn/z/ In: vvv/////////////////// FIG. 1

MULTIFILAMENT EXTRUSION METHOD AND APPARATUS BACKGROUND OF THE INVENTION The present invention relates to a multifilament extrusion method and apparatus. More particularly, the invention relates to a method and apparatus for extrusion of multifilament strands of synthetic resins. Still more particularly, the invention relates to a method and apparatus for melt spinning multifilament synthetic resin strands.

Extrusion apparatus and methods for producing multifilament strands are well known. For extruding multifilaments of synthetic resins, such as polypropylene, the extruder includes a downwardly oriented orifice for extruding a plurality of molten filaments of the synthetic resin in a downward direction. The apparatus also includes means, such as a cooling chamber, through which the, molten filaments are passed to solidify same. In order to accelerate the setting of the filaments, it is customary to employ a heat exchange medium such as ambient or cooled air which may be circulated relative to the moving strand. While such devices are well known and function commercially to produce synthetic fibers such as polypropylene, it is generally advisable to increase capacity for a given piece of equipment where possible. In extruding multifilament strands, the extrusion speed is frequently limited by the tendency of the extruded filaments to adhere to one another. In order to prevent this undesirable adhesion, extrusion speeds are generally required to be low.

It is an object of the present invention to provide an improved method and apparatus for extrusion of multifilament strands. It is a further object of the present invention to provide such an improved method and apparatus for extrusion of multifilament strands of synthetic resins. ,It is still a further object to provide an improved method and apparatus for the melt extrusion of synthetic resin filaments. It is still a further object to provide such improved method and apparatus wherein the extrusion capacity is increased.

BRIEF SUMMARY OF THE INVENTION The foregoing and other objects of the invention which will be apparent to those having ordinary skill in the art are achieved according to the present invention by providing apparatus for producing a multifilament strand comprising extrusion means comprising a plurality of downwardly directed extrusion orifices for extruding a multifilament strand in a substantially vertical downwards direction, a heat exchanger comprising a tube disposed below said extrusion orifice and disposed substantially vertically with its longitudinal axis in alignment with said extruded strand, said tube having its upper open end spaced downwardly of said extrusion orifice defining a gap therebetween and having an opening in the lower end thereof for passing the extruded strand therethrough, means for introducing a heat exchange gas into the lower portion of said tube for passage upwardly therethrough in counter-current heat exchange relationship with said strand, first baffle means located in a lower portion of said tube forming with said tube an annular chamber for guiding said heat exchange gas in an annular flow pattern flowing upwardly in said tube surrounding said strand, said first baffle means isolating said strand from said gas for a first distance adjacent the lower end of said tube and permitting said gas to flow upwardly in said annular pattern surrounding and in contact with said strand a second distance upwards of the first baffle means, and second bafile means located at the upper portion of said tube for conveying said heat exchange gas in an annular flow pattern away from the upper portion of said tube. According to the present invention, an improved method of melt spinning a multifilament strand comprises the steps of downwardly extruding a plurality of filaments of a molten fiber-forming material, forming an annular, upwardly flowing heat exchange gas flow surrounding and out of contact with said downwardly moving filaments, moving said annular gas flow upwardly surrounding and in counter-current heat exchange contact with said filaments to solidify the molten filaments, and conveying said gas in an annular fiow pattern away from the filaments.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS There follows a detailed description of a preferred embodiment of the invention, together with accompanying drawings. However, it is to be understood that the detailed description and accompanying drawings are provided solely for the purpose of illustrating a preferred embodiment and that the invention is capable of numerous modifications and variations apparent to those skilled in the art without departing from the spirit and scope of the invention;

FIG. 1 is a diagrammatic side elevation of an extrusion apparatus according to the present invention;

FIG. 2 is a top sectional view taken along the line II,II of FIG. 1;

FIG. 3 is a top sectional view taken along the line III,III of FIG. 1.

With reference to FIG. 1, an apparatus for producing a multifilament strand according to the present invention comprises an extruder 1 for extruding a multifilament strand. The extruder is of known configuration and comprises a spinneret 2 which comprises a plurality of downwardly directed extrusion orifices for extruding a multifilament strand 3 in a substantially vertical downward direction. A typical machine of this type is a Fimsai machine having a nominal capacity of 20 kilograms per hour of polypropylene. The outside diameter of the screw is milimeters and the compression ratio is l;4. The length of the diameter ratio is 20 and the maximum screw rpm is 40. The barrel temperature is 235-240 C. for polypropylene and the winding speed is 300 to 400 meters per minute. The device has two extrusion heads only one of which is shown in FIG. 1 for simplicity. The device also includes a heat exchanger 4 comprising a tube 5 disposed below extrusion orifice 2 and disposed substantially vertically with its longitudinal axis in alignment with the extruded strand. The upper open end 6 of the heat exchanger tube is spaced downwardly of the extrusion orifice thereby defining a gap therebetween. The lower end of the tube includes an opening 7 for passing the extruded strand 3 therethrough. The device also includes a blower 8 for introducing a heat exchange gas into the lower portion of the tube for passage upwardly therethrough in counter-current heat exchange relationship with the strand. A first baffle 9 located in the lower portion of the tube forms with the tube an annular chamber 10 However, it has been found that this arrangement ef-' fectively cools the molten filaments thus increasing the capacity of the machine over conventional heat exchange gas arrangements.

After the heat exchange gas assumes the annular configuration'in chamber 10, the gas moves upwardly in-said annular pattern surrounding and in contact with the strand. The heat exchange gas contacts the strand a distance B upwards of the first baffle means. This distance is chosen to provide sufficient heat exchange for setting the fibers in question according to well known principles.

The device shown in FIG. 1 includes a second baffle 1 l which is located at the upper portion of the tube for conveying heat exchange gas in an annular flow pattern away from the upper portion of the tube.

Heat exchanger tube is preferably cylindrical as shown in FIGS. 2 and 3. The lower end 12 of heat exchanger tube 5 is closed by means of a plate having an aperture therein. First baffle 9 is preferably a cylindrical tube open at both ends located concentrically with respect to the heat exchanger tube and extending through the aperture in the lower endl2 thereof to provide a passageway for strand 3.

The second baffle 11 preferably comprises a tube open at both ends, circular in section, and located concentrically with respect to the heat exchanger tube thus forming an annular conduit therebetween for conveying heat exchange gas in an annular flow pattern away from the upper portion of the heat exchanger tube. The second baffle thus preferably comprises a first cylindrical portion 13 located concentrically within the heat exchanger tube and a second portion 14 conically diverging outwardly above the upper end of the heat exchanger tube for conveying the heat exchange gas upwardly and outwardly away from the extrusion orifice. The downwardly extruded filaments 3 pass downwardly through heat exchanger tube 5 and are wound on conventional rollers 15, 16,'which may comprise draw rolls. Blower 8 introducesv a heat exchange gas, such as ambient air or air colled by means of heat exchanger 17 into cooled annular chamber in the lower portion of heat exchange tube 5. There is thus formed an annular upwardly flowing heat exchange gas surrounding and out of contact with the downwardly moving filaments. The heat exchange gas flow pattern thus formed in then moved upwardly surrounding and in counter-current heat exchange contact with said filaments in region B of the heat exchange tube to solidify the molten filaments. The gas is then conveyed along region C of the heat exchanger tube in an annular flow pattern out of contact from the filaments and out of the heat exchanger tube. In a specific example of the present invention, the extruder described in detail above having a nominal capacity of 20 kilograms per hour was operated using a conventional heat exchanger for the extruded filaments. It was found that the capacity for extruding polypropylene with cooling air at a temperature of from 2533 C. was approximately 10 kilograms per hour, or half of the nominal value assigned to the apparatus. Two strands of 50 filaments each were extruded through the two extrusion orifices of the Fimsai machine. Under identical conditions, but employing a heat exchanger according to the present invention, the capacity was increased to 27 kilograms per hour. This represents a 270 percent increase over the capacity obtained with a conventional heat exchanger and a 35 percent increase over the nominal value for the apparatus. The invention is also applicable to extrusion of other multifilament strands and is particularly applicable to melt spun strands, particularly strands of fiber-forming synthetic resins such as resins comprising olefin polymers such as polymers of the olefins ethylene or propylene exemplified by polyethylene polypropylene, and copolymers thereof.

The heat exchange gas entering the device is preferably filtered by means of one or more conventional filter screens such as screen 18 in conduit 19 from blower 8 or screen 20 in the annular chamber 10 formed between heat exchanger tube 5 and baffle tube 9.

While we do not intend to be limited to the theory of the present invention, it is believed that the improved results according to the present invention are achieved by several important factors. In the first place, the heat exchanger gas is passed as a high velocity tubular layer symmetrically around the filaments which travel in the opposite direction. This high velocity tubular layer of gas apparently reduces the pressure in the area adjacent the filaments thus tending to pull from the filaments hot air which is entrained therewith. Because this suction action is uniformly distributed around all of the filaments, the tendency is to separate the adjacent threads rather than impinge them upon one another such as a cross-current would do. Secondly, the top portion of the heat exchange tube is open and the second baffle means conically diverges outwardly above the heat exchanger tube. The purpose of the opening is to let the threads running down at high speed to exchange heat directly with ambient air and to pull this ambient air with them thus augmenting the cooling effect. The function of the diverging cone is to divert the high velocity heat exchange gas without creating turbulence in the open zone immediately below the extruder. This outwardly diverging air also creates an upward air movement that causes the hot air surrounding the hot extruder to move upwardly and away from the filaments leaving the extruder. As a result of the foregoing arrangement, the air used for cooling the filaments is effectively ambient air and does not require to be cooled. In the past, the impingement of one strand upon another has been minimized by utilizing a very low velocity gas stream. This requires, however, that the gas is cooled. According to the present invention, the gas is introduced evenly around the threads without disturbing them. Accordingly, a much larger quantity of air can be utilized resulting in no requirement for extrinsic cooling of the heat exchange gas.

What is claimed is:

1. A method of melt spinning a multifilament strand comprising the steps of: downwardly extruding a pluraiity of filaments of a molten fiber-forming material; forming an annular, upwardly flowing heat exchange gas flow surrounding and out of contact with said downwardly moving filaments; moving said annular gas flow upwardly from a lower position surrounding and in counter-current heat exchange contact with said filaments to solidify the molten filaments; and conveying said gas in an annular flow pattern away from the filaments at a position above said lower position, the distance between said positions being suflicient to effect solidification of said filaments.

2. A method according to claim 1 wherein said heat exchange gas comprises ambient air.

3. A method according to claim 1 wherein said heat exchange gas comprises cooled air.

4. A method according to claim 1 wherein said fiber- I forming material comprises a synthetic resin.

5. A method according to claim 4 wherein said resin comprises an olefin polymer.

6. A method according to claim 5 wherein said olefin comprises ethylene or propylene.

7. Apparatus for producing a multifilament strand comprising: extrusion means for exturding a multifilament strand comprising a plurality of downwardly directed extrusion offices for extruding a multifilament strand in a substantially vertical downwards direction; a heat exchanger comprising a tube disposed below said extrusion orifice and disposed substantially vertically with its longitudinal axis in alignment with said extruded strand, said tube having its upper open end spaced downwardly of said extrusion orifice and having an opening in the lower end thereof within said tube for passing the extruded strand therethrough means for introducing a heat exchange gas into the lower portion of said tube for passage upwardly therethrough in counter-current heat exchange relationship with said strand; first bafile means located in a lower portion of said tube forming with said tube an annular chamber for guiding said heat exchange gas in an annular flow pattern flowing upwardly in said tube surrounding said strand, said first bafile means isolating said strand from said gas for a first distance adjacent the lower end of said tube and permitting said gas to flow upwardly in said annular pattern surrounding and in contact with said strand a second distance upwards of the first baffle means; and second baffie means comprising a tube positioned within said heat exchanger tube forming therewith an annular chamber for isolating said strand from said gas for a second distance adjacent the upper end of said tube, said second baffie means being spaced upwardly of said first baffle means and located at the upper portion of said tube for conveying said heat exchange gas in an annular flow pattern away from the upper portion of said tube, the uppermost portion of said second baffle means being spaced downwardly of said extrusion orifice defining a gap therebetween for admitting ambient air to enter said heat exchanger tube with said strand.

8. Apparatus according to claim 7 wherein said tube is cylindrical. I

9. Apparatus according to claim 8 wherein the lower end of said tube is closed and wherein said first baffle h tiiinii'ifiii155$i1i$$l$5$al25'aii heat exchanger tube and extending through an aperture in the lower end thereof to provide a passageway for said strand, said tubes forming an annular conduit therebetween for forming said annular heat exchange gas flow pattern.

10. Apparatus according to claim 8 wherein said second baffle means comprises a further cylindrical tube open at both ends and located concentrically with respect to said heat exchanger tube to provide a passageway within said tube for said strand, said tubes forming an annular conduit therebetween for conveying said heat exchange gas in an annular flow pattern away from the upper portion of said heat exchanger tube.

11. Apparatus according to claim 10 wherein said second bafile tube comprises a first cylindrical portion located concentrically within said heat exchanger tube and a second portion conically diverging outwardly above the upper end of said heat exchanger tube for conveying said heat exchange gas upwardly and outwardly away from said extrusion orifice.

12. Apparatus according to claim 7 further including means for cooling said heat exchange gas prior to introduction to said heat exchanger tube. 

2. A method according to claim 1 wherein said heat exchange gas comprises ambient air.
 3. A method according to claim 1 wherein said heat exchange gas comprises cooled air.
 4. A method according to claim 1 wherein said fiber-forming material compriSes a synthetic resin.
 5. A method according to claim 4 wherein said resin comprises an olefin polymer.
 6. A method according to claim 5 wherein said olefin comprises ethylene or propylene.
 7. Apparatus for producing a multifilament strand comprising: extrusion means for exturding a multifilament strand comprising a plurality of downwardly directed extrusion orifices for extruding a multifilament strand in a substantially vertical downwards direction; a heat exchanger comprising a tube disposed below said extrusion orifice and disposed substantially vertically with its longitudinal axis in alignment with said extruded strand, said tube having its upper open end spaced downwardly of said extrusion orifice and having an opening in the lower end thereof within said tube for passing the extruded strand therethrough; means for introducing a heat exchange gas into the lower portion of said tube for passage upwardly therethrough in counter-current heat exchange relationship with said strand; first baffle means located in a lower portion of said tube forming with said tube an annular chamber for guiding said heat exchange gas in an annular flow pattern flowing upwardly in said tube surrounding said strand, said first baffle means isolating said strand from said gas for a first distance adjacent the lower end of said tube and permitting said gas to flow upwardly in said annular pattern surrounding and in contact with said strand a second distance upwards of the first baffle means; and second baffle means comprising a tube positioned within said heat exchanger tube forming therewith an annular chamber for isolating said strand from said gas for a second distance adjacent the upper end of said tube, said second baffle means being spaced upwardly of said first baffle means and located at the upper portion of said tube for conveying said heat exchange gas in an annular flow pattern away from the upper portion of said tube, the uppermost portion of said second baffle means being spaced downwardly of said extrusion orifice defining a gap therebetween for admitting ambient air to enter said heat exchanger tube with said strand.
 8. Apparatus according to claim 7 wherein said tube is cylindrical.
 9. Apparatus according to claim 8 wherein the lower end of said tube is closed and wherein said first baffle means comprises a further cylindrical tube open at both ends located concentrically with respect to said heat exchanger tube and extending through an aperture in the lower end thereof to provide a passageway for said strand, said tubes forming an annular conduit therebetween for forming said annular heat exchange gas flow pattern.
 10. Apparatus according to claim 8 wherein said second baffle means comprises a further cylindrical tube open at both ends and located concentrically with respect to said heat exchanger tube to provide a passageway within said tube for said strand, said tubes forming an annular conduit therebetween for conveying said heat exchange gas in an annular flow pattern away from the upper portion of said heat exchanger tube.
 11. Apparatus according to claim 10 wherein said second baffle tube comprises a first cylindrical portion located concentrically within said heat exchanger tube and a second portion conically diverging outwardly above the upper end of said heat exchanger tube for conveying said heat exchange gas upwardly and outwardly away from said extrusion orifice.
 12. Apparatus according to claim 7 further including means for cooling said heat exchange gas prior to introduction to said heat exchanger tube. 